Recent years, global environment issues due to an air pollution have emerged, and a gas detection equipment has been required to have a higher sensitivity against a background of tightened regulation of an emission gas from a factory facility or an automobile. An environmental criteria in relation to an air pollution requires, for example, NOx to be equal to or less than 40 ppb (parts per billion). Thus, an extremely small amount of gas component in the order of ppb is required to be detected. Also, apart from the environmental issues, in the field of a defense or a security, to develop an accurate and quick analytical method has been becoming a challenge ahead with respect to the NBC (nuclear: N; biological agent: B agent; chemical agent: C agent) substances. Amongst them, with regard to the C agent, as observed in the Tokyo subway sarin gas attack, it is required to quickly sense a noxious gas which has an extremely higher harm to a human body. In this regard, it is required to detect an extremely low concentration of a gas component on a real-time basis in order to prevent a secondary injury from occurring. Various methods have been known for detecting the gas component having a relatively higher concentration. In contrast, however, the detection methods are limited for detecting the gas component having a concentration of ppb (parts per billion) or ppt (parts per trillion), which corresponds to the extremely low concentration.
For example, at a disaster site or a site at which an act of terrorism occurs or the like, it is desired to sense the risk in advance by detecting the extremely small amount of the gas component. In many cases, such gas component having the extremely low concentration is detected by use of a large equipment in research facilities. In this case, a large sized installation type equipment, which is expensive and has large weight and volume, is required such as a gas chromatography or a mass spectrometer or the like. On the other hand, when direct measuring in the field is demanded, it is necessary to rely on a simplified measuring method for detecting by use of a biological reaction mechanism. Such simplified method has, however, a lot of problems of, for example, a limited storage life, temperature control, and the determination being limited to a presence or absence of the gas component. Under such circumstances, it has been demanded to provide an apparatus that is capable of detecting the gas component having an extremely low concentration on a real-time basis, in other words, an apparatus that has a smaller weight and volume and a better portability and is capable of detecting the gas component having the extremely low concentration in the order of ppt to ppb in a selective manner with higher sensitivity.
As a detection element for the gas component with low concentration, for example, a certain element has been known that has a conductive layer in which a surface of a carbon nanostructure is surface modified with an organic substance or the like capable of selectively reacting or adsorbing with a specific substance and measures a potential difference or the like which varies depending on the gas component adhered to the surface of the carbon nanostructure. In this type of detection element, for example, when a similar component or the like to the detection target gas component is immixed as an impurity in a gas obtained in air, it is likely to fail to accurately detect the detection target gas component. Furthermore, when the organic substance which functions as a detection probe strongly adsorbs the detection target gas component, after then it becomes impossible to detect the gas component again. In other words, it becomes impossible to use the detection element in a repetitive manner. For this reason, it is demanded to provide an apparatus that is capable of repetitively detecting the gas component having the extremely low concentration in a selective manner with higher sensitivity.